I think a feature that enables marking sections in the HEX view and coloring them can be really helpful for visually identifying parts of binary formats (headers, list, etc).
The way I imagine this working is selecting bytes with the mouse and right clicking, then an option like "Color this section..." appears in the context menu. Then a color picker appears and selects the new background of the selection. Of course the marking stays permanent as long as the file is open.
Thanks!